This invention relates to a hyperthermia apparatus and more particularly to an apparatus having three-dimensional (3-D) focusing capability with combined hyperthermia treatment and noninvasive thermometry capabilities.
Known hyperthermia treatment systems include multiple applicators and multiple temperature sensors for controlling the operation of the hyperthermia system. The multiple applicators utilizing ultrasound or electromagnetic energy in the direct contact operating mode are placed directly upon an elastic cooling belt containing a circulating cooling liquid to carry the heat of hyperthermia treatment away from the surface of the healthy tissue. The temperature sensors are implanted in the normal tissue in the vicinity of the tumor, as well as within the tumor. Systems involving the placement of temperature sensors within the body are referred to as invasive thermometry systems. Those persons skilled in the art desiring additional information for this system are referred to U.S. Pat. No. 4,397,314 issued Aug. 9, 1983.
A known instrument for detecting microwave energy and for giving an accurate measurement of the power density thereof is disclosed in U.S. Pat. No. 3,919,638 issued Nov. 11, 1975. This instrument is substantially unaffected by polarization or modulation of the electromagnetic waves and includes a planar array of parallel connected diode detectors each having a pair of antenna leads forming a dipole antenna. The diode array may include groups of diodes having different antenna lead lengths to detect different frequencies of microwave energy for a meter. The meter may be selectively switched between the outputs of the different groups.
Further, the potential use of multiple frequency band radiometry as a means of noninvasive sensing of one-dimensional temperature profiles is presented in an article entitled "Noninvasive Thermometry Using Multiple-Frequency-Band Radiometry: A Feasibility Study", Stavros D. Prionas and G. M. Hahn, Bioelectromagnetic 6:391-404, 1985 Alan R. Liss, Inc. The article discloses that microwave thermography has been extensively used for the detection of cancerous nodules. Operating frequencies in the range of 1.3 to 6.0 GHz (free space wavelengths in the range of 5 to 23 cm.s) have been employed. At these long wavelengths subcutaneous temperature measurement is possible and detection of superficial tumors in the brain and thyroid is, in principle, feasible.
The article further discloses that a computer tomographic approach using 10 GHz microwaves has been proposed as an alternative to mammographic examination. A self-balancing microwave radiometer for measuring the energy emitted from a heated volume within a single frequency band has been developed at the RCA laboratories. The power spectrum of thermal noise generated by a given temperature depth distribution is governed by Planck's law of blackbody radiation. The frequency spectrum of energy received at the surface of the human body is affected by the frequency dependent attenuation properties of the intervening tissues. Microwave radiometry (the technique of measuring noncoherent electromagnetic energy, in the microwave part of the spectrum, that is emitted or scattered by the medium under observation) can be used to measure the thermal noise emitted from a heated volume of biological tissue.
This article reports the analysis of the spectral content of this thermal noise and the comparison of the magnitude of the signal to the inherent threshold of noise detectability associated with an ideal microwave radiometer. In the analysis a one-dimensional temperature distribution model was assumed. In real situations, three-dimensional temperature distributions will be encountered. It is clear that to resolve such a three-dimensional temperature field with a reasonable amount of spatial resolution additional information will be needed. This additional information might be in the form of data acquired using different orientations of a signal receiving aperture or a properly phased array of receiving apertures. An intriguing alternative is to employ a phased array of receiving apertures that coherently detect the signal emanating from a point in space. In either case, well established signal processing algorithms could be used to convert the measured data to reconstruct the temperature distribution.
The use of "Radiometer Receivers for Microwave Thermography" was disclosed in an article of the same title by D. V. Land, University of Glasgow, Glasgow, Great Britain, published in the microwave journal, May 1983. A comparison or Dicke radiometer configuration is used. The receiver produces an output from the input switching that is proportional to the difference between the source temperature detected by an antenna and the temperature of an internal reference load or noise generator.
Finally, the application of broad-band correlation techniques to medical microwave thermography was studied and reported in an article entitled "The Thermal and Spatial Resolution of a Broad-Band Correlation Radiometer with Application to Medical Microwave Thermography", Joseph C. Hill et al., IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-33, No. 8, August, 1985.
An essential difference between the present invention and the invention of U.S. patent application Ser. No. 935,936, filed Nov. 11, 1986 and the background references is that the present invention is for a 3-D focusing of the energy which is accomplished by cylindrical or annular phased array. The previous annular phased arrays were capable of steering the heating pattern within the patient cross-section (target) with either power or phase steering. This feature was a primary function which resulted from the unique focusing provided by the coherent or at least synchronous EM fields which provided common polarization alignment of the electric field (E-field). The E-field in the target is the mechanism which creates the heating of the tissues. In contrast, the present invention uses at least an antenna group of at least three antennae stacked along the E-field direction and aligned with the long axis of the target. Thus, in a dipole configuration, the dipole lengths are aligned with the long axis of the target around which it is placed. This arrangement permits the heating fields to be not only focused and steered along the patient's cross-section but also along the long axis of the target.
An advantage of the 3-D hyperthermia apparatus is that in its simplest form (a single group), it allows the phase of the antennae to be set to provide a desired heating length. Another advantage is that a plurality of groups can be utilized to provide deep target heating capability. Yet another advantage is the adjustment of the phase and power of each group's elements to regulate the position of the heating region in the target.